Solar Energy Perspectives - IEA

Chapter 11: Testing the limits
estimated from traffic and road-use data. Usually, peak late-afternoon traffic occurs during the
peak electricity demand period (from 3 pm to 6 pm). According to United States statistics, even
in that period 92% of vehicles are parked and potentially available to the grid (Inage, 2010).
Figure 11.6 How EV and PHEV batteries can help level the load on the electric grids
Supply
Difference between
maximum and minimum
with load leveling
Total demand for EVs
Supply from V2G
Middle load
operation curve
Difference between
maximum and minimum
without load leveling
00:00 12:00 24:00
Hours
Source: Inage, 2010.
Key point
EVs and PHEVs used with smart grids can help integrate variable renewable electricity.
What is more likely to reduce the power capacity of a billion dispersed batteries is the capillary
nature of electric distribution systems. Although recharging stations and high-volume access
points may develop fast-charging capabilities going up to 30 kW or even higher, the electrical
hook-ups for most batteries may have a much more limited capacity – only 3 kW to 12 kW – to
exchange with the grid. Even so, with an assumed average of 6 kW and 90% batteries available
for charge, the power capacity available for avoiding curtailment would be 5 400 GW
worldwide, more than the 5 000 GW maximum excess supply from variable renewable,
estimated above as the difference between maximum wind capacity and base load.
The estimated electricity consumption for all these vehicles over a year would be about
10 000 TWh – a 50% increase over the total for electricity and hydrogen in transport in the
BLUE Map Scenario. This number suggests that almost all electricity consumption for travel
could come from variable renewables through smart grids. Some excess capacity could also
be available for EVs and PHEVs to contribute to peak demand and reduce the required
storage needs to avoid shortages.
V2G possibilities certainly need to be further explored. They do entail costs, however, as
battery lifetimes depend on the number, speeds and depths of charges and discharges, although
to different extents with different battery technologies. Car owners or battery-leasing companies
will not offer V2G free to grid operators, not least because it reduces the lifetime of batteries.
Electric batteries are about one order of magnitude more expensive than other options available
for large-scale storage, such as pumped-hydro power and compressed air electricity storage.
The cost of batteries in transport is acceptable because the total cost of the on-board stored
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© OECD/IEA, 2011